We have discovered an unusual family of interspersed repeated DNA in the Mouse. Nucleotide sequences homologous to a portion of the mouse ribosomal gene non-transcribed spacer (rDNA NTS) were found to be scattered throughout the genome and not restricted to the ribosomal gene family. One region where these interspersed rDNA NTS sequences have been specifically located is adjacent to the Mu, Gamma 2b and Alpha immunoglobulin heavy chain constant region genes. We have recently found that the mouse rDNA NTS sequence family has been conserved during evolution. Homologous sequences have been found in human rDNA NTS and elsewhere throughout the human genome. We propose to study the structure, function and evolution of this interspersed gene family. We will utilize recombinant DNA technology, restriction enzyme analysis and nucleotide sequencing to obtain detailed structural information on the interspersed rDNA NTS genes. We will focus our study on those mouse rDNA NTS sequences which are adjacent to the immunoglobulin heavy chain constant region genes. This is a novel approach and offers the advantage of being able to explore the evolution of this interspersed gene family by studying them within the context of a group of well characterized genes. Studies on the rDNA NTS sequences adjacent to the immunoglobulin genes of several different mouse species will provide the first detailed information on the evolutionary behavior of a specific subset of genes belonging to a larger interspersed DNA family. Our analysis of the structural and positional stability of the interspersed rDNA NTS sequences during evolution may provide an explanation for the dispersal of this gene family throughout the genome and lead to new information on the mobility of interspersed DNA's in mammals. The remarkable evolutionary conservation of the mouse rDNA NTS sequence family suggest that they may have a function. We will test whether they are transcribed and if they can serve as an origin of replication.